The invention relates to a circuit arrangement for the power supply of a two-wire sensor which is attached to one pole of a voltage distribution source by an initial connecting line in which a current-limiting resistor is located and is attached to the other pole of the voltage distribution source by a second connecting line, and where at least one limiting diode is positioned parallel to the two-wire sensor and the current-limiting sensor.
Two-wire sensors consist of a measuring sensor, which measures a physical magnitude such as temperature, pressure, or the field strength of a magnetic field, and of electronic components for processing the signals delivered by the measuring sensor. Both the power source and the transmission of the measured and processed measuring signals are performed by only two lines, hence the term two-wire sensor. A two-wire sensor consequently has only two terminals, which simultaneously serve the power source and the transmission of the measured and processed measuring signals.
Two-wire sensors which are employed in areas exposed to the danger of explosion are guarded by a circuit arrangement for limiting current and voltage—so-called electrical barriers. To protect against excess voltages that might cause an ignition, the two connecting lines are connected by at least one limiting diode. To protect the sensor from excess currents, which can cause the sensor to overheat, a series resistor is inserted into the circuit behind the limiting diode.
Two-wire sensors equipped with a so-called HART® interface require a so-called HART®-resistor in one of the two connecting lines leading from the power source to the two-wire sensor, however. When the two-wire sensor is heavily loaded this additional resistor in one of the connecting lines can lead to an insufficiency in the distribution voltage required for the faultless operation of the two-wire sensor.